1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device including an insulating film formed of a high dielectric constant film such as a gate oxide film of a MOSFET or a capacitive element of a memory cell; a film-forming apparatus; and a storage medium that stores therein a program for executing the method.
2. Background Art
A gate insulating film of a MOSFET has conventionally been formed of a silicon oxide (SiO2) film. By reducing a thickness of a silicon oxide film, an operation speed thereof can be improved. However, since the silicon oxide film with a smaller film thickness causes an increase in leakage current, an improvement of the operation speed is limited. Thus, a hafnium compound film (specific inductive capacity: 10–30) and a zirconium compound film (specific inductive capacity: 10 to 25) have recently been widely considered as new gate insulating films in place of a silicon oxide film. Such films have a higher dielectric constant than that of a silicon oxide film. In addition, when a physical film thickness of the films is increased, an electrical film thickness can be made small, so that a gate leakage current of a transistor can be restrained.
Japanese Patent Laid-Open Publication No. 2002-246388 (claims 1 and 6, section 0030) discloses a method of forming a hafnium oxide film by, for example, a chemical vapor deposition (CVD) using a material such as Hf alcoxide and an oxidation gas such as oxygen.
However, when a hafnium compound film is used as a gate insulating film, a problem can occur in that a flat band voltage (Vfb) of the hafnium compound film positioned below a gate electrode formed of polysilicon may shift several hundred mV (on the basis of an absolute value), as compared with a flat band voltage of a silicon oxide film being used as a gate insulating film.
The term flat band voltage is briefly described below. The flat band voltage (Vfb) is determined by a difference between a work function of an electrode and that of a substrate, and an electric charge in an insulating film. The flat band voltage can be expressed by the following equation (1).Vfb=Φm−Φs−Q0x/C0x  (1)In the equation (1), Φm is a work function of an electrode, Φs is a work function of a substrate, Q0x is an electric charge in an insulating film, and C0x is a capacity per unit area of the film.
As described above, when a hafnium compound film is used as a gate insulating film in place of a silicon oxide film, a flat band voltage of the hafnium compound film may shift several hundred mV. A reason therefor may be that a work function of a polysilicon electrode changes on account of hafnium (Hf) interposed between the polysilicon film and the hafnium compound film. Such a phenomenon may also occur in a case where a zirconium compound film is used as a gate insulating film.